[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 251436
TCDAT3

Tropical Storm Gaston Discussion Number  21
NWS National Hurricane Center Miami FL       AL082022
300 PM GMT Sun Sep 25 2022

The large convective burst that fired overnight and this morning
appears to have lead to Gaston's center reforming under the deep
convection further to the north and west. This also evident in
GOES-16 GLM lightning data that showed a clear arcing pattern
embedded in the convection prior to the new center becoming evident
on visible satellite imagery.  Since then, the convection has been
rapidly decaying, as the storm loses instability support from a
sharp upper-level trough as it moves into its axis. Subjective and
objective Dvorak numbers this morning were still CI 3.0/45-kt from
TAFB and UW-CIMSS ADT. While scatterometer data largely missed the
circulation earlier, it still showed tropical storm force winds
extending well to the northeast of the center. The initial intensity
is being maintained at 45 kt for this advisory.

Gaston, post reformation, has made its westward turn, with the
latest motion estimate at 270/10 kt. Gaston is currently situated
between an anomalously strong deep-layer ridge to its northeast, and
a more climatological ridge to its southwest. These features are
forecast to merge over the next 24-48 hours to the northwest of
Gaston, and should help steer the storm more to the west-southwest
for the remainder of its lifespan. The guidance this cycle is just a
bit further south and west compared to the previous cycle, and the
latest NHC track forecast was nudged in that direction, following
the consensus aids TVCN and HCCA.

Gaston might have had its last convective hurrah this morning, with
the GFS, ECMWF, CMC, and HWRF suggesting the storm will struggle to
produce organized convection from here on out. This could be related
to the upper-level flow pattern, where the storm is moving out of an
environment favorable for ascent into an environment favorable for
descent, limiting convection, especially as it continues to traverse
24-25C SSTs. The latest forecast still shows Gaston becoming a
post-tropical cyclone in about 24 hours, but if the convection does
not return before then, this evolution could occur sooner. The low
should persist another day or two before it opens up into a trough
in the subtropical Atlantic in about 72 hours, in agreement with the
majority of the global model guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 39.4N  36.5W   45 KT  50 MPH
 12H  26/0000Z 39.2N  38.0W   40 KT  45 MPH
 24H  26/1200Z 38.7N  39.9W   35 KT  40 MPH...POST-TROPICAL
 36H  27/0000Z 38.0N  41.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  27/1200Z 37.4N  44.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 60H  28/0000Z 36.8N  47.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  28/1200Z...DISSIPATED

$$
Forecaster Papin
This weather bulletin was brought to you by:
www.nashvilleweather.net